Foundation caisson



y 1934- H. CHAPMAN FOUNDATION CAISSON Filed March 1, 1953 Fig. I.

Air 5? Compressor Emu W n Leslie H. Chapman secured in place by bolts11.

Patented May 22, 1934 'i STATES PATENT} It is the object of thisinvention to provide a novel caisson adapted to facilitate theconstruction of subaqueous foundations in deep water or where the natureof the material beneath the water or various combinations of water andunstable bottom make the work relatively difficult with the structuresheretofore employed.

In the accompanying drawing, which illustrates the best form of myinvention at present 1 known to me;

Figure 1 is a fragmentary, vertical section through my improved caissonand showing diagrammatically the connections for supplying compressedair to the several air chambers and for regulating the pressure therein;

Fig. 2 is a similar section through a slightly modified form of theinvention;

Fig. 3 is a diagrammatic plan View of the caisson,

Fig. 4 is a fragmentary, horizontal section through the same, and

Fig. 5 is a fragmentary vertical section through the upper portion ofone of the air chambers.

The caisson has a body 5 of concrete formed with a multiplicity ofvertically extending wells 6 open at the top and bottom faces of thebody. In order to further lighten the body 5 so that it may be floatedinto place, it is formed with a series of smaller wells 7 which arepreferably closed at the bottom as indicated in Figs. 1 and 2. The wallsof the caisson at the bottom are formed with cutting edges 8 fitted withmetal caps to facilitate sinking into the soil beneath the water. Thethickness of the walls diminishes upward, said walls being made as thinas possible while having the requisite strength to resist hydrostaticpressures and at the same time properly locate the center of gravity inorder that the entire structure may float without danger of overturningwhile in the process of construction.

Each of the wells 6 is provided with a metal lining 9 extending upwardfrom the bottom a distance dependent upon the size and proportions ofthe caisson and condition of the soil into which it is to be driven. Insome cases this lining may reach to the top of the concrete body. Theupper extremity of the lining is fitted with a bulkhead 16 which isreadily removable, being Suitable gaskets 12 are placed between thebulkhead and an internal flange on the lining 9 to seal the joint. Asshown in Fig. 1, a pipe 13 communicates with the interior of the chamberformed beneath the bulkhead 10 andan air compressor 14 is arranged tosupply air under pressure through the pipe 13. A valve 15 controls anair escape pipe or port for further facilitating the regulation of theair pressure within the chamber 16. Where the compressor 14 is connectedto a number of the air chambers, each chamber may be cut oif from thecompressor by closing a valve such as the valve 17.

In the form of the invention shown in Fig. 2, a bottom 18 closes thelower end of the air chamber 16 and rests on the top of an inwardly eX-tending flange 19. The bottom 18 is held in place by air pressure Withinthe chamber 16, a suitable gasket 20 being placed between the bottom 18and flange 19. As further shown in Fig. 2, the bulkhead 10 at the top ofthe chamber 16 is sometimes fitted with an upwardly extending conduit 21having a closure or removable cap 22 on its upper end. This conduit 21may be connected to the suction pipe of a dredge to provide for theremoval of material from the chamber 16 without removing the bulkhead10. A pipe 23 communicates with the chamber 16 shown in Fig. 2 forconnection with the compressor, as in Fig. 1. The several chambers arealso provided with air pressure gauges 24 and pressure relief valves 15and 1'7.

The caisson may be built on shore and launched on launchways orconstructed on barges and supported on suitable floats until assembled.Concrete for extending the walls of the caisson upward may then bepoured. The chambers 16 are ordinarily left open at the bottom but if byreason of wave action or other cause it appears likely that varyinghydraulic pressure may cause said chambers to partially lose their airpressure then the bottoms 18 and gaskets 26 are used and sulficient airpressure is maintained in the chambers 16 to hold the bottoms 18 inplace.

The caisson is floated to the location where it is to be sunk. Accuratecontrol of the position of the caisson is maintained during this step ofthe procedure by regulating the air pressure in the several chambers 16.When the caisson is to be sunk air is allowed to escape through thevalves 15 so that the water enters the lower ends of the chambers 16. Asthe structure sinks the caisson walls may be extended upward byconstruction of suitable forms and pouring of the concrete incontinuation of the top. The top of the caisson is at all times keptabove the water level. When the caisson has been sunk so that it restson the soil beneath the water, air pressure in the chambers 16 isgradually reduced, allowing the caisson to sink into the soil and whenthe point is reached flb III

where the caisson no longer continues to sink after the air pressure isreleased, one or more of the chambers 16 is opened by removing thebulkheads 10 and also the bottoms 18 where the latter are used. This isaccomplished quickly and easily with my steel bulkheads as compared toprior caissons known to me. Excavation of the soil beneath the caissonis now accomplished by working within the open wells 6. Asthecaisson'meets increased resistance other chambers 16 may be' openedby removal of the bulkheads l0 and after all the chambers are open thedredging process is continued and the body of the caisson built up untilit has been lowered to where it rests on a sutficiently solidfoundation. Obviously, upon removal of the bulkheads 10, sinking may becontinued until the entire metal linings 9 are driven into the soilbeneath the water.

My improved caisson greatly facilitates the control of the rate ofsinking of the structure. Thus in case it sinks too fast, the airpressure in the unopened chambers 16 is merely increased until thecaisson sinks at a slower rate. If the material beneath the caisson isof such consistency as to give a tendency for one side of the caisson tosink faster than the other, the air pressure in the chambers controllingthe'buoyancy at the first side is merely increased so as to preventuneven settlement. The smaller wells '7 are filled with concrete at suchtime as the resistance of the soil beneath the caisson requires greaterweight to be brought to bear upon it in order to continue the sinking ofthe caisson into thesoil. Where the condition of the soil beneath thewater at the location of the foundation is of such consistency that itis likely to completely fill the chambers 16, the bulkheads 10 with theconduits 21 for dredging are employed. Thus if any chamber 16 becomesfilled with silt or soil the dredging may be conducted until the loosematerial is removed and thereafter air pressure may be applied in thechambers to reduce the rate of sinking of any part of the caisson.

If it is found necessary to change the location of the caisson after ithas once been sunk to the earth underlying the water, the caisson may beraised and refloated by increasing its buoyancy by the applicationofincreased air pressure in the chambers 16. Notwithstanding the facilityof control afforded by my improved caisson, it will be evident. that thelower end is free to penetrate the material encountered at the bottom ofthe water to great depths.

As hereinbefore stated, the lining 9 extends upward from the bottom ofthe caisson a distance depending on the condition of the subaqueous soiland the position of the bulkheads 10 is determined by the height of thelinings 9. A preliminary survey of the site of the pier indicates the.depth of the deposit of soft, subaqueous silt and the lining shouldextend upward a distance proportionate to the depth of such deposit,otherwise it isnecessary to employ the form of the invention shown inFig. 2 wherein dredging in the wells may be accomplished withoutremoving the bulkhead 10. In cases where the chamber 16 becomesfilledwith silt and, in the absence of such provision for dredging, removal ofthe bulkhead 10 is difiicult because of the pressure of the siltthereon. The present invention is primarily adapted for use where thepier is of such depth that pneumatic excavation is impractical. In anysuch case the air chambers of the several wells should be located in thelower portion only of the wells, that is, in the lower half thereof. Bythis arrangement a minimum of compressed air is required to fill thechambers and at the same time give the desired control during thesinking operation.

Having described my invention, what I claim as new and desire to protectby Letters Patent is: 1. A caisson for use as a foundation in subaqueoussoil comprising, a body formed with a multiplicity of wells extendingfrom top to bottom of said body and so proportioned as to permitfloating of the lower portion of the caisson, a series of removablebulkheads mounted in said wells and spaced a substantial distance fromthe lower ends thereof, said bulkheads forming air-tight chambers in thelower portions of said wells and said chambers having a depth notgreater than half the depth of the wells in the finished caisson, meansfor supplying compressed air to the several chambers and means forregulating the air pressure within'the same.

2. A caisson comprising, a body formed with a multiplicity of wellsextending from top to bottom of said body and so proportioned anddistributed as to permit floating of the caisson, a series of steelshells fixed in the lower portions of said wells, bulkheads removablysecured to the upper ends of said shells, said bulkheads and. shellsforming air-tight chambers within the lower half only of said wells andmeans for regulating the air pressure Within said chambers.

3. A caisson comprising, an integral body of concrete formed with amultiplicity of wells open at the top and bottom of said body and sodistributed and proportioned as to'permit the fioating of said body, anupwardly removable bottom in each of said wells, removable bulkheadsspaced upward from said bottoms in said wells and forming air-tightchambers in said wells and means for controlling the air pressure withinsaid chambers.

4. A caisson comprising, an integral body of concrete formed with amultiplicity ofwells extending to the top and bottom of said body, anupwardly removable bottom in each of said wells, a removable bulkheadspaced upward from said bottom and forming air-tight chambers in saidwells and means for supplying air under pressure to said chambersseverally, said bottoms being held in sealing engagement with the lowerends of said wells solely by air pressure within said chambers.

5. A caisson comprising, a body formed with a multiplicity of verticallydisposed wells, proportioned and distributed to permit the floating ofthe caisson and open at the bottom of said body to permit the dredgingof material beneath the body by the open dredging method, removablebulkheads mounted in said wells to form air-tight chambers in the lowerhalf thereof and means communicating with said chambers to permit thedredging of material within the same while retaining said bulkheads insaid wells.

LESLIE H. CHAPMAN.

